The present invention relates generally to radiation interaction measurement devices and temperature measurement devices and, more specifically, to a dual neutron flux/temperature measurement sensor which utilizes a phosphor mixture having two principal constituents, one being neutron sensitive and the other being temperature sensitive.
It is well known that emission properties of phosphors vary in accordance with temperature. This correlation has been used to devise various types of thermometry hardware. For example, surface temperature of a rotating flywheel has been measured by inducing fluorescence from a pulsed nitrogen laser in a material that includes lanthanum oxysulfide doped with europium. The temperature dependence of the phosphor emission has been shown both in amplitude and lifetime changes. With a pulsed laser as the stimulating source, either the ratio of two emission line intensities (amplitudes) or the lifetime of some selected line can be used to determine the temperature.
In the field of nuclear reactor engineering, the interactions of neutrons with nuclei are important to the release of nuclear energy in a form capable of practical utilization. Inelastic neutron collisions do not occur below energies of about 0.1 Mev, but elastic collisions between neutrons and nuclei will be effective in slowing down the neutrons until their average kinetic energy is the same as that of the atoms of a scattering medium. This energy depends on the temperature of the medium, and is thus referred to as thermal energy. Neutrons whose energies have been reduced to values in this region are designated xe2x80x9cthermal neutronsxe2x80x9d.
Phosphors have been used to measure thermal neutron flux. A mixture of boron-containing plastic and ZnS(Ag) phosphor has been used to provide a slow-neutron scintillator. A slow neutron passing through the scintillator is captured by a B10 nucleus. The resultant energetic alpha and lithium particles reach a ZnS(Ag) granule with sufficient residual energy to cause a scintillation. Light from the scintillation travels to the photomultiplier photocathode and reaches it with sufficient intensity to cause a recognizable pulse at the anode. The slow-neutron scintillators have been made by using a transparent bioplastic mold cast from a negative steel mold. In use, the surface of the scintillator faces a photomultiplier, while the opposite surface is covered with aluminum foil or other light reflective coating. See, for example, xe2x80x9cHigh Efficiency Slow-Neutron Scintillation Countersxe2x80x9d, NUCLEONICS, by K. H. Sun et al. (July, 1956).
The extreme environment of some nuclear reactor cores, with temperatures in the range of 1,000xc2x0 C., presents a difficult problem for sensing both temperature and neutron flux. A need exists for an improved sensor capable of simultaneously measuring both neutron flux and temperature.
An object of the present invention is to provide a single sensor capable of providing simultaneous measurement of both neutron flux and temperature.
Another object of the present invention is to provide a sensor which is easy to install and relatively simple in construction.
These and other objects of the invention are met by providing a dual neutron flux/temperature measurement sensor which includes a phosphor mixture having a first neutron-sensitive phosphor constituent and a second activated thermophosphor constituent coated on an end of a fiber optic, and means for detecting light generated by charged particles produced by neutron absorption in the first constituent. The first constituent produces the charged particles when neutrons are absorbed therein, and the charged particles produce scintillations in the second constituent. The scintillations of the second constituent are detected and correlated to a temperature value which varies in accordance with variations in the detected scintillations. The second constituent is preferably a rare-earth activated thermophosphor.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.